Compounds which inhibit the Ca.sup.2+ -activated potassium channel (Gardos channel) of cells are useful in the treatment of a wide variety of diseases. For example, Sickle Cell Anemia can be treated with compounds which inhibit the Ca.sup.2+ -activated potassium channel of erythrocytes (Stuart et al., J. Haematol. 86:820 (1994). In addition, agents capable of inhibiting Ca.sup.2+ -activated potassium channels have been shown to be useful in the treatment of arteriosclerosis (U.S. Pat. No. 5,358,959 to Halperin et al.) Moreover, cell proliferation is dependent on the regulated movement of ions across various cellular compartments, including activation of Ca.sup.2+ -activated potassium channels (Magni et al., J. Biol. Chem. 261:9321 (1991)). Thus, agents which inhibit Ca .sup.2+ -activated potassium channels can be used in the treatment of proliferative diseases, including cancer, blood vessel proliferative disorders, fibrotic disorders and arteriosclerotic conditions.